Google Contacts API Create New Contact in My Contacts System Group. more: https://www.mycontactsync.com/

GoogleContactService.cs

public class GoogleContactService
{
  public void CreateContact()
  {
    var cr = this.CreateContactsRequest();
    var groups = cr.GetGroups().Entries.ToList();
    var myContactsSystemGroup = groups.FirstOrDefault(x => x.SystemGroup == "Contacts");
    
    var newContact = new Contact();
    
    // ...
    
    // attempt to add to `My Contacts` system group
    if (myContactsSystemGroup != null && !String.IsNullOrWhiteSpace(myContactsSystemGroup.Id))
    {
        newContact.GroupMembership.Add(new GroupMembership() { HRef = myContactsSystemGroup.Id });
    }
    
    var createUri = this.CreateCreateContactUri();
    var createdEntry = cr.Insert(createUri, newContact);
  }
  
  private ContactsRequest CreateContactsRequest()
  {
    // todo: outside the scope of this gist
  }
  
  private Uri CreateCreateContactUri()
  {
    // todo: outside the scope of this gist
  }
}

note: this uses the Google GData Contacts nuget package: https://www.nuget.org/packages/Google.GData.Contacts

Blog post for context https://aaron-hoffman.blogspot.com/2018/01/create-google-contact-api-my-contacts-system-group.html

Project site that uses this to sync contacts between gmail accounts: https://www.mycontactsync.com/